1. Field of the Invention
The present invention relates to a carrier structure for a planetary gear system applicable for an automatic transmission of an automotive vehicle.
2. Description of the Related Art
A planetary gear system includes a sun gear as an external gear, a ring gear as an internal gear and pinion gears-meshing with the sun gear and the ring gear and rotatably supported on a carrier. When such a planetary gear system is employed in an automatic transmission, a predetermined transmission ratio is established by fixing one of the sun gear, the internal gear and the carrier, for example.
One example of the carrier structure of the planetary gear system is partially illustrated in FIG. 13. As shown, the carrier structure includes a pinion shaft 31 rotatably supporting a pinion gear 30, a carrier body 32 fixedly supporting the pinion shaft 31, needle bearings 33 interposed between the internal periphery of the pinion gear 30 and the external periphery of the pinion shaft 31. Between opposite end faces of the pinion gear 30 and the carrier body 32, a plain washer 34 and a locking washer 36 provided with a plain bearing member 35 on a sliding surface are interposed. A tip end of a locking portion 37 of the locking washer 36 is bent to engage with an engaging recess portion 38 formed in the carrier body 32.
Also, a conventional carrier structure of a planetary gear system has been disclosed in Japanese Patent Application Laid-Open No. 141483/1993. In the disclosed construction, the planetary gear system includes a pinon shaft rotatably supporting a pinion gear, a carrier body fixedly supporting the pinion shaft, needle bearings interposed between the inner periphery of the pinon gear and the external periphery of the pinion shaft and pinion washers disposed between opposite end faces of the pinion gear and the carrier body and fitted on the outer periphery of the pinion shaft to support the thrust load on the pinion gear. A flange extends from the inner peripheral edge of each of the pinion washers in the axial direction. The flange is inserted between the internal periphery of the pinion gear and the external periphery of the pinion shaft for bearing the thrust load of the needle bearing.
However, in the case of the carrier structure of the planetary gear system illustrated in FIG. 13, addition of the locking washer 36 should cause the locking washer 36 to slide at a rotation speed of the pinion gear 30 to make a pV (pressure.times.velocity) value greater. Therefore, it becomes necessary to add the plain washer 34 between the pinion gear 30 and the locking washer 36 so that sliding is caused between the pinion gear 30 and the plain washer 34 and between the plain washer 34 and the locking washer 36 to lower the pV value (particularly, average slip speed V). thus requires a greater amount of parts by addition of the plain washer and so forth to cause lowering assembling ability.
On the other hand, in the case of the carrier structure of the conventional planetary gear system as disclosed in Japanese Patent Application Laid-Open No. 141483/1993, support for the thrust load of the pinion gear is born by the pinion washer. Therefore, heat generation amount is large thus degrading durability.